Correlation between NDI, PROMIS and SF-12 in cervical spine surgery

Abstract

Background context: As the focus in spine surgery has shifted from radiographic to patient-centric outcome, patient-reported outcomes measures (PROMs) are becoming increasingly important. They are linked to patient satisfaction, and are used to assess healthcare expenditure, determine compensation and evaluate cost-effectiveness. Thus, PROMs are important to various stakeholders, including patients, physicians, payers, and healthcare institutions. Thus, it is vital to establish methods to interpret and evaluate these outcome measures.

Purpose: To evaluate the correlation between Neck Disability Index (NDI), Patient Reported Outcome Measurement Information System Physical Function (PROMIS-PF) and Short Form-12 Physical Health Score (SF-12 PHS) in cervical spinal surgery in order to determine the validity of PROMIS-PF in these patients.

Study design/setting: Retrospective review of prospectively collected data.

Patient sample: Consecutive patients who underwent cervical surgery for degenerative spinal pathology with a minimum of 3 months follow-up.

Outcome measures: Self-reported measures that is, PROMs including NDI, PROMIS-PF, and SF-12 PHS.

Methods: No funding was received for this study. The authors report no relevant conflict of interest. PROM collected preoperatively and at each follow-up were analyzed using Pearson product-moment correlation.

Results: Of the 121 patients included, 66 underwent anterior cervical discectomy and fusion, 42 cervical disc replacement, 13 posterior cervical decompression with or without fusion. A statistically significant improvement was achieved in all PROMs by 6 weeks and maintained at 1 year. Furthermore, the percentage of patients achieving an improvement greater than minimum clinically important difference was similar for NDI and PROMIS-PF, particularly at a follow-up of 3 months or more. A statistically significant negative correlation was seen between NDI and PROMIS-PF, which was moderate preoperatively and in the early postoperative period (r=-0.565 to -0.600), and strong at 3 months or longer follow-up (r=-0.622 to -0.705). A statistically significant, negative correlation was also seen between SF-12 PHS and NDI, which was moderate preoperatively and at 6 weeks (r=-0.5551 to -0.566); and strong at all other time-points (r=-0.678 to -0.749). There was a statistically significant positive correlation between SF-12 PHS and PROMIS-PF, which was strong to very-strong at all time-points (r=0.644-0.822), except at 2 weeks (r=0.570).

Conclusions: Although NDI and SF-12 have been used for several years, PROMIS is a new outcome measure that is increasingly being implemented. The results of our study demonstrate the convergent and discriminant validity of PROMIS-PF, supported by the strong correlation between SF-12 PHS and PROMIS-PF at all time-points and the moderate correlation between NDI and PROMIS-PF preoperatively and in the early postoperative period, respectively. Thus, while PROMIS-PF may not be a good surrogate for disease-specific outcome measures, it may extend value as a precise and efficient general health tool.

Keywords: Cervical; NDI; PROMIS-PF; Patient reported outcomes; SF-12; Spine surgery.